The tooling used in such industries is appropriately referenced as perishable tooling and includes, but is not limited to, such tooling components as shot sleeves, ladles, inner and outer tips, runners, dies, and mold cavities. Some of such tooling is virtually constantly in contact with molten metals having temperatures ranging up to 1400xc2x0 F. and beyond, and the conventional steel tooling tends to rapidly corrode and erode. Extreme heat, coupled with the pressures used in the process, tend to cause rapid oxidation of the tooling and its rapid decomposition or deterioration. During the time when the corroded tooling is being removed and replaced, the machinery is down and unproductive.
Cooling of the tooling in the work environment is not a practical answer for the problem because it causes premature solidification of the metal being cast, resulting, for example in improper filling of the molds and unacceptable castings.
While many steels have been evaluated in attempts to promote life cycle improvement for such tooling, H-13 Hot Work Die Steels have proven to be the most cost-effective material to use. The typical life of a shot sleeve made from this material is about 40,000 cycles, or approximately a period of three to four weeks in a normal production facility. In molds used in the pressure casting industry, which also need frequent replacement, various ceramic and cermet molds have also been tried with little success. The ceramics and cermets are susceptible to fracture from impact stresses and the compressive stresses induced during the heat-up or cool-down phases of operating the equipment.
The present invention is concerned with both machining an underlying metal substrate to provide an undercut or isolated surface with relation to the dimensions desired and then filling the undercut, first with a thermally compatible interface system capable of marrying a wear resistant ceramic coating to the metal, and finally with the ceramic coating which contacts the molten metal at the high temperatures of the metal. The ceramic coating barrier has low thermal conductivity and is resistant to the corrosive action of the molten metal at the high temperatures involved. It not only provides a highly wear resistant surface for the molten metals and various moving parts to impinge upon, it provides an insulating characteristic which allows the tooling part to be cooled without transferring that cooling to the molten metal. This attribute reduces the oxidizing effect of the molten metal on the surface of the component without deleteriously affecting the temperature of the molten pool of cast metal. The ceramic barrier further well resists oxidation and provides a very low co-efficient of friction surface for the molten metals and tooling parts to thereby reduce adhesive and abrasive wear on the tooling parts.
Magnesium zirconate ceramic, and various other thermally insulative ceramic barriers to be identified herein have been employed, or are expected to be employed, as the tooling component contact surface. Cobalt chromium alloy material has been well employed as an interface or bonding layer, and other interface layers expected to be employed will also be identified herein. In some instances, it has been found desirable to utilize an intermediate layer or layers between the initial coating and the ceramic barrier surface which will also be identified.
After surface preparation, as by shot blasting and cleaning, the interface coating is applied to the tooling component using a standard plasma deposition or high velocity, high oxygen fuel deposition device and, after the interface barrier is applied and fused to the metal, the ceramic barrier is applied, using a standard plasma deposition system or any other suitable particulate deposition system. Thereafter, the surface of the ceramic is polished to provide a glass-smooth surface which is free of imperfections and has a coefficient of friction that is as low as possible.
It is a principal object of the invention to provide a new technology for molten material contacting tooling of the type mentioned, which compositely utilizes machining techniques in combination with a composite barrier material of high integrity which the machining entraps or isolates in a manner to protect the edges of the barrier material.
A further object of the invention is to provide tooling which has a greatly extended service life and provides tooling components which are harder, tougher, more wear resistant, and far more durable.
Still another object of the invention is to provide a method of manufacturing tooling of the character described which is far more economical to utilize considering both the cost of replacement of the tooling and the machinery downtime which accumulates with the present day, far more frequent replacement of tooling components.
Other objects and advantages of this invention will become apparent with reference to the accompanying drawings and the accompanying descriptive matter.